1. Field of the Invention
The present invention relates to a toner for electrostatic-image development, which is used for image formation of an electrophotographic method.
2. Description of the Related Art
In recent years, in order to further save energy in the image forming device of an electrophotographic method, there has been required a toner for electrostatic-image development (which hereinafter may be simply referred to as a “toner”) with which heat fixing can be performed at a lower temperature. In such a toner, in order to achieve more excellent low-temperature fixing property and stably form a high quality image over a long period of time, there has been required a toner that satisfies long-term stability of charging.
For example, there is widely known a toner that contains a crystalline material as a fixing aid, specifically, a crystalline ester compound such as a crystalline polyester resin or a fatty acid ester compound (for example, see Patent Literature 2).
However, in the toner containing the fixing aid as disclosed in Patent Literature 1, when the compatibility between the crystalline ester compound and the binder resin at the time of heat fixing is high, there arises a problem in which the plasticity of the binder resin proceeds before the heat fixing and this causes the heat-resistant storability of the toner to be degraded, whereas, when the compatibility is low, there are problems in which it is not possible to obtain sufficient low temperature fixing property, and the crystalline ester compound is liberated to be exposed to the surface of toner particles, the charging of the toner is lowered and thus an image failure such as a decrease in image density or fogging occurs.
In order to solve such problems, it is proposed that by the control of the compatibility between a binder resin and a crystalline ester compound, the crystalline ester compound is caused to exist in a crystallized state in toner particles, and the crystalline ester compound and the binder resin are made compatible with each other at the time of heat fixing, with the result that both low-temperature fixing property and long-term stability of charging are obtained (see Patent Literatures 2 and 3).
However, in fact, with the toner as described above, it is not possible to sufficiently satisfy the requests for low-temperature fixing property, heat-resistant storability and long-term stability of charging, which are being increasingly made.